The present invention relates generally to a method and apparatus for mass centering of a rotary body referred to herein as a rotor.
Mass centering is a process for finding an axis of rotation for a rotor such that the axis of rotation passes through the center of the net mass of the rotor which is distributed within same, so that the net distribution of mass of the rotor is symmetrical about the axis of rotation. The axis that thus passes through the center of mass of the rotor is referred to as the axis of inertia of the rotor.
Thus, the process for mass centering of a rotor by means of a mass centering machine involves ascertaining the position of the axis of inertia which extends through the center of mass of the rotor. The position of the axis of inertia is indicated by marking the point at which that axis passes through the end faces of the rotor. That is conventionally effected by means of centering bores which are produced in the ends of the rotor at the points at which the axis of inertia passes therethrough.
When effecting mass centering in one plane, that is to say when the primary axis of inertia is ascertained by measuring the static unbalance of the rotor, the axis of inertia extends parallel to the axis of rotation of the rotor. It is then sufficient for the position of the axis of inertia to be indicated by marking on only one end face of the rotor. Particularly when dealing with rotors which are of a generally disk-like configuration, it is sufficient to ascertain the position of the axis of inertia by measuring the static unbalance, that position thus being derived from the result of the unbalance measuring operation and the weight of the rotor.
In a typical method and apparatus for mass centering of a rotor, once the position of the axis of inertia has been ascertained, it is then necessary to move a marking tool which is generally in the form of a drill relative to the rotor, in a radial direction with respect to the axis of rotation of the rotor and parallel to the axis of rotation. A high level of accuracy and a high resolution capability is required on the part of the mechanical unit operable to produce that relative movement.
U.S. Pat. No. 4,644,792 discloses a method and apparatus for determining the mass center of a body, in which a high degree of resolution can be achieved. However major components of the mechanical system must be produced with a very high level of precision in order for the mechanical unit provided to produce the above-mentioned relative movement to afford the high resolution capability required.